1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head for use in thermally-assisted magnetic recording to write data on a recording medium with the coercivity thereof lowered by irradiating the recording medium with near-field light.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head unit including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider configured to slightly fly above the surface of a recording medium. The slider has a medium facing surface configured to face the recording medium. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end).
Here, the side of the positions closer to the leading end relative to a reference position will be referred to as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be referred to as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, disadvantageously reduces the thermal stability of magnetization of the magnetic fine particles. To resolve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To resolve the foregoing problems, there has been proposed a technology called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near the medium facing surface of the slider.
U.S. Pat. Nos. 8,284,637 B2 and 8,456,968 B1 each disclose a technology in which the surface of the core of the waveguide and the surface of the plasmon generator are arranged to face each other with a gap therebetween, so that evanescent light that occurs from the surface of the core based on the light propagating through the core is used to excite surface plasmons on the plasmon generator to generate near-field light based on the excited surface plasmons.
In a thermally-assisted magnetic recording head that employs a plasmon generator as a source of generation of near-field light, the write head unit includes a coil, a main pole and the plasmon generator. The coil produces a magnetic field corresponding to data to be written on a recording medium. The main pole has an end face located in the medium facing surface. The main pole passes a magnetic flux corresponding to the magnetic field produced by the coil, and produces a write magnetic field from the aforementioned end face. The plasmon generator includes a near-field light generating section located in the medium facing surface. To provide a magnetic recording device with higher linear recording density, it is preferred that the end face of the main pole and the near-field light generating section of the plasmon generator be located close to each other in the medium facing surface.
U.S. Pat. Nos. 8,284,637 B2 and 8,456,968 B1 each disclose a structure in which at least part of the main pole is located between the medium facing surface and the front end face of the core closest to the medium facing surface. This structure allows the end face of the main pole and the near-field light generating section of the plasmon generator to be located close to each other in the medium facing surface.
In a thermally-assisted magnetic recording head, the plasmon generator and the main pole become hot due to heat generated by the plasmon generator. This can cause the plasmon generator to be deformed or broken, and cause the main pole to be oxidized or corroded, thus shortening the life of the thermally-assisted magnetic recording head.
The aforementioned structure disclosed in U.S. Pat. Nos. 8,284,637 B2 and 8,456,968 B1 causes the main pole to rise in temperature due to not only the heat generated by the plasmon generator but also light that emerges from the front end face of the core and enters the main pole. The aforementioned structure thus has the problem that the main pole is particularly susceptible to damage.